It is very likely they will use the keyboard action from Tyros 1...thus providing a marginally better key feel than the 3k, and also to allow for aftertouch,a feature already on the entry level synths.
It wouldn't add much weight and the R&D has been paid for and it has been tested already by T1 owners.Most if not all buyers of the 3k replacement would be happy with such a positive change.
Ian